Solid rocket propellants containing boron carbide as fuel



3,009,800 SOLID ROCKET PROPELLANTS CONTAINING BORON CARBIDE AS FUEL Jerome Swimmer, 3855 W. Carmen Ave, Chicago, Ill. No Drawing. Filed Mar. 17, 1958, Ser. No. 721,677 4 Claims. (Cl. 52.5)

This invention relates to new and improved rocket propellant compositions. More particularly, this invention relates to new and improved solid rocket propellant compositions. In one specific aspect thereof, this invention relates to new and improved solid, cast in place, case bonded rocket propellant compositions.

The general principles governing the behavior of rocket propellants have now been fairly completely elucidated. Broadly, rocket propellant systems may be divided into two main types, (1) those in which the oxidizer and the fuel are separately delivered to the combustion chamber and (2) those in which the combustion chamber is produced with a mixture of the oxidizer and fuel present therein. Each type exhibits characteristic advantages and disadvantages. Thus, with type 1 devices it is necessary that both the oxidizer and the fuel be fluids (either gaseous or liquid) and that separate storage, delivery and metering systems be provided, one for the fuel and one for the oxidizer, resulting in a considerable degree of mechanical complexity. However, since the fuel and oxidizer are maintained separate until the two are finally mixed in the combustion chamber, a rather wide selection of possible fuel-oxidizer systems is available although the selection is considerably restricted in view of the requirement that each member of the system pair be either a gas or a liquid.

In type 2 the oxidizer-fuel mixture may be pressed or cast in place in the combustion chamber. This avoids the necessity for separate storage, delivery and metering systems for the oxidizer and the fuel. Since this mixed charge burns from the inside outward, the unburned portion of the charge serves to define the combustion chamher and also protects the rocket case from flame impingement until near the very end of the combustion process, thereby making possible a comparatively simple combustion chamber design. However, since in this type of device the oxidizer and fuel are in intimate contact over long periods of time, it is obvious that only a relatively few oxidizer-fuel combinations possess the requisite stability for such use.

I have found that boron carbide is an excellent fuel component of solid rocket propellant compositions.

Boron carbide is easily made by well known electric furnace techniques and is readily available at a reasonable cost.

Boron carbide has a very high combustion enthalpy, some 22,200 Btu. being evolved per pound of boron cmbide in the reaction:

4 2 2 3 p- -iz The very high heat of combustion of this material, coupled with the very high density of boron carbide (2.54) results-in the evolution of no less than 3,530,000 Btu. on combustion of one cubic foot of the material, a figure that is very close to the maximum obtainable, either actually or theoretically, by the combustion of elements or compounds. The average molecular weight of the combustion products resulting from the burning of boron carbide with oxygen is 61.1.

One object of this invention is to provide high energy rocket propellent compositions.

Another object of this invention is to provide high energy solid rocket propellant compositions.

3,009,800 Patented Nov. 21, 1961 Additional objects of this invention will become apparent as the description thereof proceeds.

In accordance with one method for accomplishing the objects of this invention, an intimate mixture of boron carbide and a solid oxidizing agent is cast or compressed into the case defining the boundries of the ultimate combustion chamber of the rocket or similar device. Preferably, the slug comprising boron carbide-solid oxidizing agent is provided with a cavity of suitable size and shape forming the boundries of the initial combustion chamber. The general principles involved in the design of such cavities in the propellant slug are now well understood and firequently the propellant slug takes the form of a mnltiperforated cylinder. On ignition, the boron oarbide oxidizing agent mixture reacts on the entire inner surface of the propellant cavity and the unburned surface of the propellant charge defines the combustion chamber and the unburned portion of the propellant charge insulates and protects the rocket case from flame until near the very end of the combustion process.

The boron carbide-solid oxidizing agent mixtures of this invention are very stable and rockets are similar devices charged with such cast or compressed mixtures can be stored for any desired period without deterioration and without danger of premature ignition. The stability of these mixtures is so great that a powerful igniter is required to initiate the reaction between the components thereof. This igniter may consist, for example, of a shaped mass of black powder in contact with the propellant mixture proper, the black powder mass being permeated with electric matches which are set off when desired by passage of an electric current therethrough.

The boron carbide component of the mixtures of this invention is preferably employed in finely divided form which facilitates reaction with the solid oxidizing agent and results in complete combustion of the boron carbide. The average particle size of the boron carbide component is preferably about 44 microns or less, ranging downward to a particle size of about two microns or even less.

' If desired, rockets or similar devices may be provided with a slug of dense boron carbide which is consumed when desired by introduction of a fluid (i.e., gaseous or liquid) oxidizing agent such as oxygen, white fuming nitric acid, red fuming nitric acid or the like into the boron carbide zone through appropriate delivery and metering devices. As before, the slug of dense boron carbide may be provided with a cavity of suitable size and shape forming the boundries of the initial combustion chamber. Furthermore, a large portion or all of the fluid oxidizer delivery device may be constructed from boron carbide. Thus, the slug of dense boron carbide may be provided with one or a plurality of generally axial perforations of suitable size and location through which the fluid oxidizing agent moves from the storage vessel therefor to the previously mentioned combustion chamber. By such a system, a portion or all of the delivery system for the oxidizing agent consists of the fuel component and is consumed during operations with greatly enhanced efliciency in comparison with systems employing a conventional delivery system (eg of alloy steel pipe) which either is not consumed during operations or, if consumed, evolves comparatively little energy in the process. If desired, pipes for the delivery of the fluid oxidizing agent and even metering devices for the control of the delivery thereof may be made from boron carbide which devices are consumed during operations. Boron carbide compacts in the form of non-porous elements (e.g. pipe, metering devices and parts therefor, and the like) may be prepared by either sintering finely divided boron carbide in an inert (eg. argon) atmosphere or by hot pressing finely divided boron carbide.

For the better understanding of this invention the fol- 3 lowing illustrative but non-limiting examples thereof are given:

Example 1 Eight and one half parts by weight finely divided boron carbide were stirred into one hundred parts by weight ammonium nitrate maintained at a temperature just above its melting point. The resulting uniform suspension was poured into the propellant case of a rocket which contained a suitable core for the production of the desired initial combustion chamber. After solidification of the boron carbide-oxidizer mixture this core was removed with resulting formation of a cavity of the desired size and shape in the solidified mixture.

This propellant charge is comparatively cheap and exhibits quite good processing characteristics. However, the combustion enthalpy attainable from this mixture is only moderately high, especially when calculated on the basis of a unit volume of the solidified mixture.

Example 2 Eleven and one half parts by weight boron carbide having an average particle size of about 2 microns was intimately mixed with one hundred parts by weight finely divided ammonium perchlorate, the resulting mixture being compressed into the propellant case of the rocket.

This propellant mixture exhibits somewhat less favorable processing characteristics than the mixture of Example 1 but the mixture of the present example is appreciably superior with respect to attainable combustion enthalpy.

Example 3 Twenty six parts by Weight finely divided boron carbide were added with stirring to one hundred parts by weight lithium percholorate heated to a temperature just above its melting point. The resulting uniform suspension was poured into a cored propellant case of a rocket. After solidification of the mixture the core was removed with resulting formation of an initial combustion cavity of the desired size and shape in the solidified mixture.

This propellant mixture, while the most expensive of the three solid fuel-oxidizer mixtures here considered by to just above the melting point of the lithium perchlorate while maintaining pressure on the ram. The assembly was then cooled and the ram withdrawn.

In the production of the final operative unit, a fluid oxidizing agent storage vesselis located on the rocket nose side of the above described fuel slug. During operation, the fluid oxidizing agent is delivered from this storage vessel through a metering device and to the entrance of the axialperforation in the fuel slug. The fluid oxidizing agent travels through this axial perforation to the cavity located at the rocket nozzle side of the fuel slug. Combustion of boron carbide occurs through reaction with the fluid oxidizing agent, the fundamental reaction being stabilized and catalyzed by reaction with the lithium perchlorate present. Obviously, during consumption of the fuel slug, the fluid oxidizing agent delivery device is consumed with simultaneous release of energy that aids in propulsion of the total device. 7

Be it remembered, that while this invention has been described in connection with specific examples and specific details thereof, these examples and details are illustrative only and. are not to be considered limitations on the spirit or scope of said invention except in so far as these may be incorporated in the appended claims.

I claim:

1. The composition of matter consisting essentially of a substantially uniform mixture of boron carbide with at least the amount of an oxidizing agent selected from the group consisting of ammonium nitrate, ammonium perchlorate and lithium perchlorate stoichiometrically required for the conversion of the boron carbide to a mixture of boron oxide and carbon dioxide.

2. The composition of matter consisting essentially of i a substantially uniform mixture of boron carbide and at i a substantially uniform mixture of boron carbide and at means of specific examples is by far the most eflicient of the three. The mixture of the present example exhibits very satisfactory processing characteristics, being even superior to the mixture of Example 1 in this respect. The attainable combustion enthalpy of this mixture is much higher than those of the mixtures of Examples 1 and 2, the superiority of the mixture of the present example being especially great when the enthalpies are calculated on the'basis of a unit volume of the several solid mixtures.

Example 4 An intimate mixture of one hundred parts by weight finely divided boron carbide and fifty parts by weight finely divided lithium perchlorate was introduced into the combustion zone of a rocket case. This mixture was compressed by a ram provided with a protuberance which produced an axial perforation through the resulting com pressed powder mixture and a cavity defining the initial combustion chamber. The resulting assembly was heated least the amount of ammonium perchlorate stoichiometrically required for the conversion of the boron carbide to a m-ixtureof boron oxide and carbon dioxide.

4. The composition of matter consisting essentially of v a substantially uniform mixture of boron carbide and at least the amount of lithium perchlorate stoichmetrically required for the conversion of the boron carbide to a mixture of boron oxide and carbon dioxide.

References Cited in the file of this patent UNITED STATES PATENTS V v V 7 OTHER REFERENCES Ridgway: Boron Carbide, preprint 66-27, The Elec- 1 trochemical Societyfrom a paper presented September 1934 at the 66 General Meeting for release Oct. 1, 1934. Zaehringer: Solid Propellant Rockets, American Rocket Co., Box 1112, Wyandotte, Mich. (1955), pp. 5, 6. 

1. THE COMPOSITION OF MATTER CONSISTING ESSENTIALLY OF A SUBSTANTIALLY UNIFORM MIXTURE OF BORON CARBIDE WITH AT LEAST THE AMOUNT OF AN OXIDIZING AGENT SELECTED FROM THE GROUP CONSISTING OF AMMONIUM NITRATE, AMMONIUM PERCHLORATE AND LITHIUM PERCHLORATE STOICHIOMETRICALLY REQUIRED FOR THE CONVERSION OF THE BORON CARBIDE TO A MIXTURE OF BORON OXIDE AND CARBON DIOXIDE. 